The present invention relates to a flexural-mode tuning-fork type quartz crystal resonator used in an electronic device.
Conventionally, an electronic device such as a computer, cellular phone, or compact information device includes a piezoelectric vibrator or piezoelectric oscillator as an electronic component. The piezoelectric vibrator or piezoelectric oscillator is used as a reference signal source or clock signal source. In addition, the piezoelectric vibrator or piezoelectric oscillator incorporates a flexural-mode tuning-fork type quartz crystal resonator made of crystal.
Japanese Patent Laid-Open No. 2008-301297 discloses a conventional flexural-mode tuning-fork type quartz crystal resonator using crystal as a piezoelectric material. This related art will be described with reference to FIGS. 6 and 7.
A conventional flexural-mode tuning-fork type quartz crystal resonator 400 includes a piezoelectric chip 410, excitation electrodes 421a, 421b, 422a, and 422b, frequency adjusting metal films 424a and 424b, connection electrodes 423a and 423b, and leading wiring patterns 425 and 426.
As shown in FIG. 7, the piezoelectric chip 410 includes a flat proximal portion 411 having an almost rectangular shape when viewed from the upper side, and a pair of vibrating arm portions 412 projecting in the same direction from one side of the proximal portion 411. The pair of vibrating arm portions 412 include a first vibrating arm portion 412a and a second vibrating arm portion 412b. 
As shown in FIG. 6, the excitation electrodes 421a are provided on the upper and lower principal surfaces of the first vibrating arm portion 412a opposed to each other. Note that the “upper and lower principal surfaces” are the two surfaces of the proximal portion 411 which have the largest surface areas and are parallel to each other, and also include surfaces directed in the same direction as that of the two surfaces. Surfaces that are visible in FIGS. 6 and 7 are “upper surfaces”, and hidden surfaces are “lower surfaces”. The definitions of “upper and lower principal surfaces”, “upper surfaces”, and “lower surfaces” also apply to the description of the embodiments and FIGS. 1, 2, 4, and 5.
The excitation electrodes 421b are provided on the two side surfaces of the first vibrating arm portion 412a opposed to each other. The excitation electrodes 422a are provided on the upper and lower principal surfaces of the second vibrating arm portion 412b opposed to each other. The excitation electrodes 422b are provided on the two side surfaces of the second vibrating arm portion 412b opposed to each other.
Note that the excitation electrodes 421b provided on the two side surfaces of the first vibrating arm portion 412a are electrically connected by the frequency adjusting metal films 424a. The excitation electrodes 422b provided on the two side surfaces of the second vibrating arm portion 412b are electrically connected by the frequency adjusting metal films 424b. 
The connection electrodes 423a are provided on the upper and lower principal surfaces of the proximal portion 411 on a side close to the first vibrating arm portion 412a. The connection electrodes 423a are electrically connected to the excitation electrodes 421b, as well. The connection electrodes 423a are electrically connected to the excitation electrodes 422a of the second vibrating arm portion 412b via the excitation electrodes 421b by the leading wiring patterns 426 provided on the principal surfaces of the proximal portion 411.
The connection electrodes 423b are provided on the upper and lower principal surfaces of the proximal portion 411 on a side close to the second vibrating arm portion 412b. The connection electrodes 423b are electrically connected to the excitation electrodes 421a as well by the leading wiring patterns 425 provided on the principal surfaces of the proximal portion 411. The connection electrodes 423a are electrically connected to the excitation electrodes 422b of the second vibrating arm portion 412b. 
The frequency adjusting metal films 424a are provided at the distal end portions of the upper principal surface and the side surfaces of the first vibrating arm portion 412a, and electrically connected to the excitation electrodes 421b provided on the two side surfaces of the first vibrating arm portion 412a. The frequency adjusting metal films 424b are provided at the distal end portions of the upper principal surface and the side surfaces of the second vibrating arm portion 412b, and electrically connected to the excitation electrodes 422b provided on the two side surfaces of the second vibrating arm portion 412b. 
In the flexural-mode tuning-fork type quartz crystal resonator 400, when an alternating voltage is applied to the connection electrodes 423a and 423b, electric fields of opposite polarities are generated on the first vibrating arm portion 412a and the second vibrating arm portion 412b. The first vibrating arm portion 412a and the second vibrating arm portion 412b expand and contract so as to generate a vibration.
However, if the vibration leaks from the vibrating arm portions 412 to the proximal portion 411, the temperature characteristic and CI (Crystal Impedance) value of the flexural-mode tuning-fork type quartz crystal resonator 400 degrade.
Japanese Utility Model Laid-Open No. 51-138076 proposes a technique of forming, in the principal surfaces of the proximal portion 411, shallow groove-shaped concave portions extending in the widthwise direction, i.e., the direction perpendicular to the direction of the vibrating arm portions 412 projecting form the proximal portion 411 so as to attenuate the vibration leaked from the vibrating arm portions 412 and prevent the vibration from propagating.
However, the flexural-mode tuning-fork type quartz crystal resonator having no support arm portions as part of constitute elements cannot sufficiently attenuate the vibration leaked from the vibrating arm portions 412 even when the shallow groove-shaped concave portions extending in the widthwise direction of the proximal portion 411 are formed. It is therefore impossible to sufficiently suppress degradation in the temperature characteristic or CI value.